Disorders of arousal, attention, and information processing are widespread after traumatic brain injury, and are responsible for much of the long-term cognitive disability. However, there is little agreement about the nature of these disorders, the appropriate tasks for their assessment, nor their precise relationship to real-world functional behaviors. This project will study a large sample (140) of patients with recent traumatic brain injuries. Each patient will be studied in detail using single-case experimental methodology. The studies will assess 4 proposed dimensions of core attentional function (sustained arousal, phasic arousal, distractibility, and speed of information processing), using computerized reaction time tasks. Patients will also be videotaped engaging in naturalistic behaviors that require attention, in distracting environments. A subsample will receive follow-up testing 5-6 months later to assess attentional changes during recovery. Another subsample will be tested on and off medications thought to affect attention. The interrelationships among the 4 dimensions of core attentional function, and their relationship to naturalistic behavior will be examined using correlational techniques, multiple regression, and factor and cluster analysis. Anticipated results of the project include: 1. Establishment of the interrelationships or independence among the 4 hypothesized dimensions of core attentional function 2. Establishment of the relationship between performance on these four dimensions and complex naturalistic behavior 3. Formulation of tentative neuroanatomic hypotheses regarding control of these attentional dimensions 4. Development of a predictive model that allows prognostication of later attentional function from early test results 5. Validation of a clinically useful attention testing protocol